Isocitrate dehydrogenases (IDHs) are an enzyme group that converts isocitrate to 2-oxoglutarate (α-ketoglutarate). This enzyme group is further divided into NAD+ dependent isocitrate dehydrogenases (EC 1.1.1.41) and NADP+ dependent isocitrate dehydrogenases (EC 1.1.1.42).
IDH1 (isocitrate dehydrogenase 1 (NADP+), soluble) protein and IDH2 (isocitrate dehydrogenase 2 (NADP+), mitochondrial) protein are enzymes that are classified into the NADP+ dependent isocitrate dehydrogenases (EC 1.1.1.42). IDH1 gene mutations or IDH2 gene mutations have been found in various cancers. Specific examples thereof can include glioma and glioblastoma, acute myeloid leukemia, myelodysplastic syndrome, myeloproliferative tumor, peripheral T-cell lymphoma, chondrosarcoma, osteosarcoma, bile duct cancer, primitive neuroectodermal tumor, B-cell lymphoblastic lymphoma, malignant melanoma, prostate cancer, colorectal cancer, and thyroidal cancer (Non Patent References 1 to 16).
Also, a great majority of Ollier's disease or Maffucci syndrome patients often having chondrosarcoma have been reported to naturally retain a mosaic IDH1 gene mutation or IDH2 gene mutation (Non Patent References 8 and 9).
Features common in various literature reports are that the gene mutations in IDH1 and IDH2 are point mutations and the mutation sites are focused on amino acids important for the enzymatic reactions or amino acids close thereto. Particularly, a mutation to substitute arginine at the 132-position (hereinafter, indicated as R132) of the IDH1 protein by another amino acid accounts for a great majority of the IDH1 gene mutations. As an example, a mutation to convert arginine at the 132-position to histidine (indicated as R132H) or a mutation to convert this arginine to cytosine (R132C), leucine (R132L), serine (R132S), glycine (R132G), valine (R132V), or the like has been found to occur frequently. In addition, cases where a mutation occurs in G97, R100, H133, A134, or the like are known. The IDH2 gene mutations are mostly mutations to convert R140 or R172 to another amino acid. For example, R140Q mutation or R172K or R172S mutation is known. A great majority of mutation cases also indicate that one of the alleles resides in a wild-type form. Such features of the mutations suggest that the mutated IDH1 gene and the mutated IDH2 gene function as activating mutations.
From the functional analysis of IDH1R132H protein, it has been reported that the IDH1R132H protein has enzymatic activity totally different from that of wild-type IDH1, i.e., has the activity of converting 2-oxoglutarate and NADPH to D-2-hydroxyglutarate (hereinafter, referred to as 2-HG) and NADP+ (Non Patent Reference 17). 2-HG has been produced at a high concentration in glioma or acute myeloid leukemia cells or cultured cells having a mutation such as R132H, R132S, R132C, R132G, or G97D of IDH1, or R140Q or R172K of IDH2. Similar reports have also been made as to other IDH1 mutations (Non Patent References 18 to 20). From these reports, the possibility is suggested that mutant IDH1 protein expressed in a tumor influences the properties of the tumor via 2-HG produced by the enzymatic activity different from that of wild-type IDH.
It has been shown that acute myeloid leukemia cell line TF-1 cells caused to express IDH1R132H can grow even in a medium free from GM-CSF (granulocyte macrophage colony-stimulating factor). It has also been shown that TF-1 cells expressing IDH1R132H are hindered from differentiating into erythrocytes through erythropoietin (Non Patent Reference 21). From such reports, it is suggested that tumors are induced by the function of mutant IDH1 protein to have properties such as promoted growth or suppressed differentiation.
In patients with the aforementioned Ollier's disease or Maffucci syndrome as well, a high concentration of 2-HG is reportedly detected. There is also a report stating that IDH1 gene mutations were detected in some D-2-hydroxyglutaric aciduria patients (Non Patent Reference 22). Thus, 2-HG produced by mutant IDH protein also seems to contribute to the pathologic conditions of these diseases.
Against this backdrop, drugs inhibiting the activity of the mutant IDH1 protein have been expected to be useful as therapeutic drugs that specifically act on diseases related to IDH1 mutations, such as cancers.
Amide derivatives (Patent References 6, 7, and 8), bicyclic compounds (Patent Reference 9), aminopyridine derivatives (Patent References 10 and 11), aminopyrimidine derivatives (Patent Reference 12), and the like have been reported as compounds inhibiting the activity of the mutant IDH1 protein.
However, there is still a demand for the development of a compound with a novel structure having excellent inhibitory activity against the mutant IDH1 protein.